DESCRIPTION (adapted from the Abstract): Adolescent have among the highest rates of sexually transmitted diseases of any age group, and many current AIDS cases were infected with HIV while still in their teens, attributable to risky sexual behaviors initiated during adolescence. Intervention strategies are implemented within communities or institutions and the mechanisms by which these social contexts influence individual sexual risk-raking behaviors are poorly understood. The purpose of this study is to examine the determinants of STD and HIV acquisition among this vulnerable population incorporating the influences of the multiple social contexts within which young people live their daily lives. The specific aims of the project are to: (1) test empirically a set of hypothesis derived from an innovate conceptual model that treats the risk of STD/HIV acquisition as a sequence of interrelated behavior, beginning with initiation of sexual activity, and including the effects of intervening sexual risk-taking behaviors; (2) explore the interrelationships between sexual initiation intervening risk-taking behaviors, and STD/HIV outcomes within a multi-level conceptual framework; (3) test cross-level interactions with a view specifically to the fit of family and neighborhood characteristics, and the impact of divergent characteristics on risk-related behaviors; and (4) develop an analytic model using statistical methodology that reflects accurately the real complexity of the processing being modeled, allow for potential heterogeneity of contexts and behaviors. The National Longitudinal Study of Adolescent Health (Add Health) will be used for the analysis. The conceptual approach incorporates a multi-level perspective and draws from various strands of sociological and social psychological theories. The empirical models explicitly account for possible endogenous effects of sexual behaviors and risk of STD's, selection effects, and the embedded nature of the contexts.